An air suspension utilizing compressible characteristic of air is often used for realizing sophisticated control in connection with an electronic control device because it is comparatively easier to change the suspension characteristics.
Such control items include adjustment of body height or adjustment of vehicle attitude and can be realized by supplying the adequate amount of air to the air chamber of air suspension of each wheel and exhausting the air therefrom. However, for the sophisticated suspension control, it is essential to adequately change the supply or exhaust rate of air in accordance with respective control purposes. For instance, when it is required to increase only the body height, it is desirable that the air supply rate to the air chamber of air suspension of each wheel is not so quick in order to eliminate any shock to crews. On the contrary, a quick supply rate of air is desirable for stabilizing attitude of vehicle during running on curved road. In other cases, it is also desired by the driver to change the rate of adjustment of body height.
In order to change the supply rate of air to the air suspension depending on purposes, a device where the reservoir tanks are provided to reserve the compressed air in the circuit and two systems of paths, a small diameter pipe and a large diameter pipe, are provided to connect such reservoir tanks to the air chambers of the suspension unit of respective wheels (Japanese Laid-open Pat. No. 119623/1985).
However, the system of the prior art explained earlier requires two systems of pipings and therefore is complicated. Particularly, since a passenger car requires sophisticated control of attitude, individual supply and exhaust of air are required for the air suspension of each wheel, but the system mentioned above requires many pipings and generates a problem of increased weight.